The present invention relates to a circuit for generating a reference voltage, and more specifically to an integrated circuit for generating a reference voltage which is in agreement with a band gap of a semiconductor material that forms the transistor and which assumes a predetermined value irrespective of the temperature.
The reference voltage must, usually, assume a constant value independently of the temperature. This requirement can be satisfied by using a band-gap reference circuit. As represented, for example, by an integrated circuit LM 117 manufactured by National Semiconductor Co., the band-gap reference circuit consists of a first transistor and a second transistor of which the bases are commonly connected and which are supplied with an equal current from a current mirror circuit, the area of the emitter of the second transistor being N times greater than that of the first transistor. Further, a first resistor is connected to the emitter of the second transistor, and a connection point between the other end of the first resistor and the emitter of the first transistor is grounded via a second resistor. The collector voltage of the first transistor, on the other hand, is fed back to the power supply of the current mirror circuit via a feedback amplifier, and the output voltage is taken out from the base potential of the first and second transistors.
In such a conventional circuit for generating the reference voltage, the potential of the power supply for supplying a current to the current mirror circuit must be higher than the collector potential of the first transistor. When the reference voltage is 1.2 volts, the potential of the power supply of the current mirror circuit must be greater than 2.1 volts at room temperature. The potential of the power supply of the current mirror circuit is supplied from the power supply of the feedback amplifier. Therefore, the feedback amplifier requires a higher power-supply voltage. The requirement of such a high power-supply voltage is not desirable for integrated circuits.